Shift control unit of electric-power assist transmission

ABSTRACT

A shift control unit is provided in an electric-power-assist transmission which offers good operatability. A shift disabling unit employs a neutral-position detecting unit, a vehicle-speed judging unit, an engine-rotational-speed judging device, an OR circuit and an AND circuit. The neutral-position detecting unit is used for outputting an &#34;H&#34;-level signal to indicate that a gear is placed at a neutral position. The vehicle-speed judging unit generates an &#34;H&#34;-level signal for a speed of a vehicle equal to or higher than 10 km/h. On the other hand, the engine-rotational-speed judging device generates an &#34;H&#34;-level signal for a rotational speed of an engine equal to or higher than 3,000 rpm. The OR circuit generates an &#34;H&#34;-level signal when the vehicle-speed judging unit generates an &#34;H&#34;-level signal or the engine-rotational speed judging device generates an &#34;H&#34;-level signal. On the other hand, the AND circuit generates an &#34;H&#34;-level signal when the neutral-position detecting unit generates an &#34;H&#34;-level signal and the OR circuit also generates an &#34;H&#34;-level signal. With the AND circuit outputting the &#34;H&#34;-level signal, the shift disabling unit prevents a shift change from being made.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shift control unit for anelectric-power-assist transmission. In particular, the present inventionrelates to a shift control unit wherein a gear shift as well as theoperations to put a main clutch in an engaged or disengaged state arecarried out electrically. More specifically, the present inventionrelates to a shift control unit wherein a shift change is disabled ifthe speed of the vehicle or the rotational speed of the engine and ashift position of the gear satisfy conditions for disabling a shiftchange in spite of the fact that a shift switch has been turned on.

2. Description of the Background Art

In the conventional transmission, a gear shift is carried out byoperating both a clutch pedal (or a clutch lever) and a shift-changelever. On the other hand, in an electric-power-assist transmissiondisclosed in Japanese Patent Laid-open No. Hei 5-39865, a gear shift iscarried out electrically by a motor. In the conventional technologiesdescribed above, a shift drum is intermittently rotated in bothdirections by a driving motor so as to actuate a desired shift fork in agearshift-change operation. On the other hand, it is possible to put theclutch in an engaged or disengaged state also by using a motor as well.

In such a case, when thinking of the conventional manual transmission,only by repeating the shift-change operation can the shift change beeventually completed even if the gear is not shifted smoothly. Inaddition, whether or not the clutch can be put in an engaged statesmoothly after the shift change much depends on the operation of theclutch carried out by the driver.

As described above, in the conventional manual transmission, most ofpoor operatability as evidenced by whether or not a shift change can becompleted without repeating the shift-change operation or whether or notthe clutch can be put in an engaged state smoothly much depends on howthe operation is carried out by the driver. In other words, the driver'slearning effects allow good operatability to be obtained.

By driving both the clutch and the shift-change lever by means a motor,on the other hand, elements dependent on the operation carried out bythe driver do not exist any more. Thus, in a state where a gear shift isimpossible, if the clutch is not put in an engaged state smoothly or notin accordance with the driver's intention, it is quite within the boundsof possibility that the driver feels a sense of incompatibility.

In an electric-power-assist transmission, for example, a shift changecan be made with ease by merely operating a switch. For this reason,while cruising at a high speed or while the engine is rotating at a highrotational speed, it is quite possibile that the gear may be shifted toa neutral position by mistake, causing a relatively strong engine braketo work. As a result, a heavy load is borne by the engine.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to solve the problemsdescribed above by providing a shift control unit to be employed in anelectric-power-assist transmission offering good operatability.

In order to achieve the object described above, the present inventionprovides a shift control unit to be employed in an electric-power-assisttransmission wherein a shift change is disabled if the speed of avehicle or the rotational speed of an engine and a shift position of thegear satisfy conditions for disabling a shift change in spite of thefact that a shift switch has been turned on.

According to the configuration described above, since a shift change isdisabled when conditions for disabling a shift change are satisfied inspite of the fact that a shift switch has been turned on, the problemcaused by an incorrect operation of the shift switch can be avoided.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention, and wherein:

FIG. 1 is a plan diagram showing an operation unit of a vehicle on whichthe electric-power-assist transmission provided by the present inventionis mounted;

FIG. 2 is a diagram showing a partial cross section of the configurationof major components employed in a driving system of theelectric-power-assist transmission provided by an embodiment of thepresent invention;

FIG. 3 is a conceptual diagram showing a state in which the sleeve andthe gear are engaged with each other;

FIG. 4 is a diagram showing a perspective view of the sleeve provided bythe present invention;

FIG. 5 is a diagram showing a perspective view of the gear provided bythe present invention;

FIG. 6 is a diagram showing an enlarged portion of a outwardly-directedcog of the sleeve;

FIG. 7 is a diagram showing an enlarged portion of a inwardly-directedcog of the gear;

FIG. 8 is a diagram showing a state in which the outwardly-directed cogof the sleeve and the inwardly-directed cog of the gear are engaged witheach other;

FIG. 9 is a diagram showing a perspective view of the conventionalsleeve;

FIG. 10 is a diagram showing a perspective view of the conventionalgear;

FIG. 11 is a functional block diagram showing a shift disabling system;

FIG. 12 is a diagram showing a model of engagement timing of theconventional sleeve and the conventional gear;

FIG. 13 is a diagram showing a model of engagement timing of the sleeveand the gear provided by the present invention;

FIG. 14 is a block diagram showing the configuration of major componentsemployed in a control system of the electric-power-assist transmissionprovided by the embodiment of the present invention;

FIG. 15 is a block diagram showing a typical configuration of an ECUemployed in the control system shown in FIG. 14;

FIG. 16 is a diagram showing Part I of a flowchart provided by theembodiment of the present invention;

FIG. 17 is a diagram showing Part II of a flowchart provided by theembodiment of the present invention;

FIG. 18 is a diagram showing Part III of a flowchart provided by theembodiment of the present invention;

FIG. 19 is a diagram showing Part IV of a flowchart provided by theembodiment of the present invention;

FIG. 20 is a diagram showing Part V of a flowchart provided by theembodiment of the present invention;

FIG. 21 is a diagram showing Part VI of a flowchart provided by theembodiment of the present invention;

FIG. 22 is a diagram showing operational timing charts of a shiftspindle provided by the present invention;

FIG. 23 is a diagram showing operational timing charts of the rotationalangle of a shift spindle and the rotational speed of the engine providedby the present invention in a shift-up operation;

FIG. 24 is a diagram showing operational timing charts of the rotationalangle of a shift spindle and the rotational speed of the engine providedby the present invention in a shift-down operation; and

FIG. 25 is a diagram showing a relation between a PID (Proportional,Integral and Differential) sum value and a duty ratio.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will become more apparent from a careful study ofthe following detailed description of a preferred embodiment withreference to accompanying diagrams showing the embodiment. FIG. 1 is aplan diagram showing an operation unit of a vehicle on which theelectric-power-assist transmission provided by the present invention ismounted.

As shown in the figure, the operation unit comprises a shift-up switch51 for the electric-power-assist transmission and a shift-down switch 52also for the electric-power-assist transmission, a dimmer switch 53 forchanging the direction of a front light, a lighting switch 54 forturning on and off the front light, a start switch 55 for starting theengine and a stop switch 56 for stopping the engine. In the presentembodiment, pressing the shift-up switch 51 once will raise the shiftposition by one stage. On the other hand, pressing the shift-down switch52 once will lower the shift position by one stage.

FIG. 2 is a diagram showing a partial cross section of the configurationof major components employed in a driving system of theelectric-power-assist transmission provided by an embodiment of thepresent invention.

In the configuration shown in the figure, a driving motor 1 which servesas an electric actuator rotates a shift spindle 3 in a normal orreversed direction through a reduction gear mechanism 2. The rotationalposition (or the angle) of the shift spindle 3 is sensed by an anglesensor 28 which is installed at one end of the shift spindle 3. A clutcharm 6 extends perpendicularly to the shift spindle 3. At one end of theclutch arm 6, there is provided a gear mechanism 8 for converting therotational movement of the shift spindle 3 into a rectilinear movement.When the shift spindle 3 is rotated away from a neutral position by thedriving motor 1, the gear mechanism 8 releases the engaged state of amain clutch 5 without regard to the direction of the rotation in thecourse of the rotation. Clutch arm 6 and gear mechanism 8 are indicatedgenerally as a transmission mechanism 12, which serves to put the mainclutch 5 in an engaged or disengaged state in a manner which ismechanically coupled with the rotation of the shift spindle 3. When theshift spindle 3 is rotated back to reach the neutral position in theopposite direction, on the other hand, the engaged state of the mainclutch 5 is restored in the course of the rotation in the reverseddirection. The clutch arm 6 and the gear mechanism 8 are configured sothat the engaged state of the main clutch 5 is released at a point oftime the shift spindle 3 is rotated by a predetermined angle oftypically +/-6 degrees.

One end of a master arm 7 fixed on the shift spindle 3 is engaged with ashift clutch mechanism 9 which is installed on a shift-drum mechanism15. When the shift spindle 3 is rotated by the driving motor 1, a shiftdrum 10 is rotated in a direction determined by the rotational directionof the shift spindle 3. The master arm 7 and the shift clutch mechanism9 form such a clutch mechanism that, when the shift spindle 3 is rotatedaway from the neutral position in either direction, the master arm 7 andthe shift clutch mechanism 9 get engaged with the shift spindle 3,rotating the shift drum 10 and, when the shift spindle 3 is rotated backto the neutral position, the engaged state of the master arm 7 and theshift clutch mechanism 9 with the shift spindle 3 is released, leavingthe shift drum 10 at a position where the engaged state is released. Themaster arm 7, shift clutch mechanism 9, shift drum 10 and shift-drummechanism 15 are indicated generally as gear shifting mechanism 13,which acts to switch gears in a manner which is mechanically coupled tothe rotation of the shift spindle 3.

The edge of each shift fork 11 is engaged with an external circumferencegroove 31 of one of sleeves 30 to be described later by referring toFIG. 4. When the shift drum 10 is rotated, the shift forks 11 are movedby the rotation of the shift drum 10 in a direction parallel to theaxial direction of the rotation, moving one of the sleeves 30 determinedby the rotational direction and the rotational angle of the shift drum10 in a direction parallel to a main shaft 4.

FIG. 4 is a diagram showing a perspective view of the sleeve 30 insertedin a state slidable in the axial direction of the main shaft which isnot shown in the figure. On the circumference side surface of the sleeve30, a groove 31 is provided in the circumferential direction. The edgeof a shift fork 11 cited earlier is engaged with the groove 31. Aplurality of outwardly-directed cogs 32 are provided on a ring-shapedflange 33 to form a single body on the circumference of the shaft holeof the sleeve 30. The outwardly-directed cogs 32 are engaged withinwardly-directed cogs 42 of a gear 40 to be described by referring toFIG. 5.

FIG. 5 is a diagram showing a perspective view of the gear 40 supportedrotatably at a predetermined position on the main shaft which is notshown in the figure. A plurality of the inwardly-directed cogs 42 areprovided on a ring-shaped flange 43 to form a single body on thecircumference of the shaft hole of the gear 40. As described above, theinwardly-directed cogs 42 are engaged with the outwardly-directed cogs32 of the sleeve 30. FIG. 3 is a conceptual diagram showing a state inwhich the outwardly-directed cogs 32 of the sleeve 30 and theinwardly-directed cogs 42 of the gear 40 are engaged with each other.

On the other hand, FIG. 9 is a diagram showing a perspective view of theconventional sleeve 38, and FIG. 10 is a diagram showing a perspectiveview of the conventional gear 48. As shown in FIG. 9, a plurality ofstand-alone outwardly-directed protrusions 39 are provided on the sleeve38 concentrically with respect to the shaft hole of the gear 48. Inorder to assure the strength of each of the stand-aloneoutwardly-directed protrusions 39, however, the area of the bottomsurface of each of the stand-alone outwardly-directed protrusions 39must be made relatively large. As a result, with the conventionaltechnology, the ratio of the width of each of the outwardly-directedprotrusions 39 to the length of the circumference on which theoutwardly-directed protrusions 39 are provided increases, allowing onlyfour outwardly-directed protrusions 39 to be created thereon as shown inFIG. 9. This holds true of slits 49 bored on the gear 48 shown in FIG.10.

FIG. 12 is a diagram showing a model of relative positions of anoutwardly-directed protrusion 39 on the conventional sleeve 38 and aslit 49 on the conventional gear 48. As shown in the figure, the widthD2 of the slit 49 in the rotational direction is about twice the widthD1 of the outwardly-directed protrusion 39. As a result, a period Taduring which the outwardly-directed protrusion 39 cannot be engaged withthe slit 49 is long in comparison with a period Tb allowing theoutwardly-directed protrusion 39 to be put in an engaged state with theslit 49. The state of engagement of the outwardly-directed protrusion 39with the slit 38 is referred to hereafter as an engagement state.

In the case of the present embodiment, on the other hand, theoutwardly-directed cogs 32 are provided on a ring-shaped flange 33 toform a single body. Thus, as shown in FIG. 13, the width D3 of theoutwardly-directed cog 32 and the width D4 of the inwardly-directed cog42 in the rotational direction can be made sufficiently small, yet withadequate strength maintained. FIG. 13 shows a model of engagement timingof the relative positions of an outwardly-directed cog 32 on the sleeve30 provided by the present embodiment and an inwardly-directed cog 42 onthe gear 40 provided by the present invention. As a result, the periodTa during which the engagement state is impossible is short incomparison with the period Tb making an engagement state possible,increasing the probability of the engagement state. In this case, theengagement state is a state of engagement of the outwardly-directed cog32 with a slit 46 on the gear 40.

In addition, in the present embodiment, the difference between the widthD5 in the rotational direction of the slit 46 and the width D3 in therotational direction of the outwardly-directed cog 32 can be made small,allowing the play after the engagement of the outwardly-directed cog 32with the slit 46 to be reduced. As a result, the magnitude of a shiftshock and the amount of noise generated in the engagement can also bedecreased.

In addition, in the present embodiment, the taper of theoutwardly-directed cog 32 is bent to form a convex shape as shown inFIG. 6, while the taper of the inwardly-directed cog 42 has astraight-line shape as shown in FIG. 7. Thus, the cogs 32 and 42 can bebrought into line contact with each other in the axial direction asshown in FIG. 8, allowing concentration of stress to be avoided. As aresult, the cog strength can be increased substantially and, at the sametime, the durability and the resistance against abrasion can also beimproved as well.

In the configuration described above, the sleeves 30 are moved inparallel by the shift forks 11 to a predetermined position, causing theoutwardly-directed cogs 32 on one of the sleeves 30 to be put in anengaged state with the slits 46 of the gear 40. In this engagementstate, the gear 40 which has been supported in an idle state so far withrespect to the main shaft is engaged with the main shaft by the sleeve30, being rotated synchronously with the main shaft as is generallyknown. As a result, a rotating force transferred from a clutch shaft toa countershaft is transferred to the main shaft by way of the gear. Itshould be noted that both the clutch shaft and countershaft are notshown in the figure.

It is worth noting that, while not shown explicitly in the figure, theengine of the vehicle employing the electric-power-assist transmissionadopting the shift control method provided by the present invention is afour cycle engine. In a power transmission system for transferring powerfrom the crankshaft to the main shaft, a power output by the engine istransferred through a centrifugal clutch on the crankshaft and a clutchon the main shaft. Thus, for an engine rotational speed lower than apredetermined value, the centrifugal clutch on the crankshaft stops thetransfer of power to the clutch on the main shaft. As a result, the gearcan be shifted to any speed if the vehicle is in a halted state.

FIG. 14 is a block diagram showing the configuration of major componentsemployed in a control system of the electric-power-assist transmissionprovided by the embodiment of the present invention and FIG. 15 is ablock diagram showing a typical configuration of an ECU 100 employed inthe control system shown in FIG. 14.

As shown in FIG. 14, the driving motor 1 described earlier is connectedbetween motor+ and motor- pins of the Electronic Control Unit (ECU) 100.Sensor-signal pins S1, S2 and S3 are connected respectively to avehicle-speed sensor 26 for sensing the speed of the vehicle, an Nesensor 27 for sensing the rotational speed Ne of the engine, and theangle sensor 28 described earlier for sensing the rotational angle ofthe shift spindle 3. Shift-instruction pins G1 and G2 are connected tothe shift-up and shift-down switches 51 and 52 described earlier.

A battery 21 is connected to a main pin of the ECU 100 through a mainfuse 22, a main switch 23 and a fuse box 24. The battery 21 is alsoconnected to a VB pin through a fail-safe (FIS) relay 25 and the fusebox 24. An excitation coil 25a of the fail-safe relay 25 is connected toa relay pin.

As shown in FIG. 15, the main and relay pins of the ECU 100 areconnected internally to a power-supply circuit 106 which is connected toa CPU 101. The sensor-signal pins S1, S2 and S3 are connected to inputpins of the CPU 101 through an interface circuit 102. Theshift-instruction pins G1 and G2 are connected to input pins of the CPU101 through an interface circuit 103.

A switching circuit 105 comprises a FET (1) and a FET (2) connected inseries and a FET (3) and a FET (4) also connected in series. The seriescircuit of the FET (1) and the FET (2) and the series circuit of the FET(3) and the FET (4) are connected to each other to form a parallelcircuit. One terminal of the parallel circuit is connected to the VB pinwhile the other terminal is connected to a GND pin. The junction pointbetween the FET (1) and the FET (2) is connected to the motor- pin whilethe junction point between the FET (3) and the FET (4) is connected tothe motor+pin. The FETs (1) to (4) are selectively controlled by pulsewidth modulation (PWM) by the CPU 101 through a predriver 104. Thecontrol of the FETs (1) to (4) carried out by the CPU 101 is based on acontrol algorithm stored in a memory unit 107.

Next, the shift control method implemented by the electric-motor-assisttransmission provided by the present invention is explained by referringto flowcharts shown in FIGS. 16 to 21 and operational timing chartsshown in FIG. 22.

The flowchart shown in FIG. 16 begins with a step S10 to form a judgmentas to whether or not either the shift-up or shift-down switch 51 or 52has been operated. If one of the switches is found turned on, the flowof control goes on to a step S11 to form a judgment as to whether it isthe shift-up switch 51 or the shift-down switch 52 that has been turnedon. If it is the shift-up switch 51 that has been turned on, the flow ofcontrol proceeds to a step S13. If it is the shift-down switch 52 thathas been turned on, on the other hand, the flow of control proceeds to astep S12 at which the rotational speed Ne of the engine is stored in avariable Ne1. The flow of control then continues to the step S13.

At the step S13, the FETs employed in the switching circuit 105 of theECU 100 are selectively controlled by PWM in dependence on whether it isthe shift-up switch 51 or the shift-down switch 52 that has been turnedon starting from a point of time T1 of the time chart shown in FIG. 22.To be more specific, if it is the shift-up switch 51 that has beenturned on, the FETs (2) and (4) are controlled by PWM at a duty ratio of100% with the FETs (1) and (3) turned off. As a result, the drivingmotor 1 starts to rotate in a shift-up direction, driving the shiftspindle 3 also to rotate in the shift-up direction as well in a mannerinterlocked with the driving motor 1.

If it is the shift-down switch 52 that has been turned on, on the otherhand, the FETs (1) and (3) are controlled by PWM at a duty ratio of 100%with the FETs (2) and (4) turned off. As a result, the driving motor 1starts to rotate in a shift-down direction, a direction opposite to theshift-up direction, driving the shift spindle 3 also to rotate in theshift-down direction as well in a manner interlocked with the drivingmotor 1.

By setting the duty ratio at 100% in this way, the speed of the shiftcan be increased, allowing the duration of the shift to be shortened. Asa result, the clutch can be put in a disengaged state in a short periodof time. It should be noted that the present embodiment is designed sothat, by rotating the shift spindle by merely five to six degrees, theclutch can be put in a disengaged state.

The flow of control then goes on to a step S14 at which a first timernot shown in the figure is started to measure time. Then, the flow ofcontrol proceeds to a step S15 at which a rotational angle θ₀ of theshift spindle 3 detected by means of the angle sensor 28 is read in.Subsequently, the flow of control goes on to a step S16 to compare thedetected rotational angle θ₀ with a first reference angle θ_(ref) whichis set at +/-14 degrees in the case of the present embodiment. To bemore specific, the flow of control proceeds to the step S16 to form ajudgment as to whether or not the rotational angle θ₀ exceeds thereference angle θ_(ref). More specifically, the judgment formed at thestep S16 is a judgment as to whether or not the rotational angle θ₀ isequal to or greater than 14 degrees, or the rotational angle θ₀ is equalto or smaller than -14 degrees. It should be noted that, in thefollowing description, the phrase stating "a quantity goes beyond a +/-value" is used to imply that either the quantity is equal to or greaterthan the + value, or the quantity is equal to or smaller than thevalue - for the sake of expression simplicity.

An outcome of the judgment formed at the step S16 indicating that therotational angle θ₀ goes beyond 14 degrees means that it is quite withinthe bounds of possibility that the sleeves moved in parallel by theshift forks 11 have arrived at a normal engaged (engagement) position.In this case, the flow of control goes on to a step S17. On the otherhand, an outcome of the judgment formed at the step S16 indicating thatthe rotational angle θ₀ does not go beyond +/-14 degrees means that itis quite within the bounds of possibility that the sleeves moved inparallel by the shift forks 11 have not arrived at the normal engaged(engagement) position. In this case, the flow of control goes on to astep S30 to be described later.

When the fact that the sleeves moved in parallel by the shift forks 11have arrived at the normal engaged (engagement) position is detected ata point of time t2 as a result of the comparison of the rotational angleθ₀ with the reference rotational angle θ_(ref), the flow of controlproceeds to the step S17 at which the first timer is reset. The flow ofcontrol then continues to a step S18 at which the FETs employed in theswitching circuit 105 of the ECU 100 are selectively controlled by PWMin dependence on whether it is the shift-up switch 51 or the shift-downswitch 52 that has been turned on. To be more specific, if it is theshift-up switch 51 that has been turned on, the FETs (1) and (4) arecontrolled by PWM at a duty ratio of 100% with the FETs (2) and (3)turned off. If it is the shift-down switch 52 that has been turned on,on the other hand, the FETs (2) and (4) are controlled by PWM at a dutyratio of 100% with the FETs (1) and (3) turned off. As a result, theinput pins of the driving motor 1 are short-circuited, providing arotational load to the driving motor 1. In this state, a braking effectis applied to the driving force working in the shift-up or shift-downdirection of the shift spindle 3, reducing the magnitude of an impact ofthe shift spindle 3 on a stopper. Such an impact is generated when theshift spindle 3 is brought into contact with the stopper. It should benoted that the rotational angle of the shift spindle 3 at which theshift spindle 3 is brought into contact with the stopper is 18 degrees.

The flow of control then goes on to a step S19 shown in FIG. 17 at whicha second timer not shown in the figure is started to measure time. Then,the flow of control proceeds to a step S20 to form a judgment as towhether or not the time measured by the second timer has exceeded 15 ms.If the time measured by the second timer has not exceeded 15 ms, theflow of control continues to a step S21 to execute control of therotational speed Ne of the engine to be described later. The processingat the steps S20 and S21 are repeated until the time measured by thesecond timer exceeds 15 ms. As the time measured by the second timerexceeds 15 ms at a point of time t3, the flow of control goes on to astep S22 at which the second timer is reset.

Subsequently, the flow of control proceeds to a step S23 at which theFETs employed in the switching circuit 105 of the ECU 100 areselectively controlled by PWM in dependence on whether it is theshift-up switch 51 or the shift-down switch 52 that has been turned on.To be more specific, if it is the shift-up switch 51 that has beenturned on, the FETs (2) and (4) are controlled by PWM at a duty ratio of70% with the FETs (1) and (3) turned off. If it is the shift-down switch52 that has been turned on, on the other hand, the FETs (1) and (3) arecontrolled by PWM at a duty ratio of 70% with the FETs (2) and (4)turned off. As a result, since the sleeves are pushed against the gearby a relatively weak torque, the load borne by each cog is reduced untilthe engaged (engagement) state is reached, allowing the engagement stateto be sustained with a high degree of reliability.

The flow of control then goes on to a step S24 at which a third timernot shown in the figure is started to measure time. Then, the flow ofcontrol proceeds to a step S25 to form a judgment as to whether or notthe time measured by the third timer has exceeded 70 ms . If the timemeasured by the third timer has not exceeded 70 ms , the flow of controlcontinues to a step S26 at which the control of the rotational speed Neof the engine is executed. The pieces of processing at the steps S25 andS26 are repeated until the time measured by the third timer exceeds 70ms . As the time measured by the third timer exceeds 70 ms at a point oftime t4, the flow of control goes on to a step S27 at which the thirdtimer is reset. The flow of control then proceeds to a step S28 to startclutch-on control to be described later.

It should be noted that the time-up time of the third timer adopted inthe present embodiment is determined from the period Ta during which anengaged state cannot be established as described earlier by referring toFIG. 13. To put it in detail, the time-up time of 70 ms is set so thatthe control to push the sleeves against the gear is executed at leastuntil the period Ta is over. In the meantime, the outwardly-directedcogs are brought into contact with the inwardly-directed cogs. Since theduty ratio has been reduced to 70%, however, the load borne by each cogis light, being favorable to the strength of the cog.

In addition, the time-up time of the third timer does not have to be setat a fixed value. The time-up time can be set at a variable valuedetermined as a function of gear setting. For example, the time-up timeis set at 70 ms and 90 ms for the gear set at the range first to thirdspeeds and the range fourth to fifth speeds respectively.

If the outcome of the judgment formed at the step S16 shown in FIG. 16indicates that the rotational angle θ₀ has not exceeded the firstreference angle θ_(ref), on the other hand, the flow of control goes onto the step S30 shown in FIG. 18 to form a judgment as to whether or notthe time measured by the first timer has exceeded 200 ms. Since theoutcome of the judgment formed for the first time indicates that thetime measured by the first timer has not exceeded 200 ms, the flow ofcontrol goes on to a step S31 at which the Ne control is executed beforereturning to the step S16 shown in FIG. 16.

As time goes by, the outcome of the judgment formed at the step S30indicates that the time measured by the first timer has exceeded 200 ms,implying that the shift change attempted this time ends in a failure. Inthis case, the flow of control goes on to a step S32 at which the firsttimer is reset. The flow of control then proceeds to a step S33 at whichthe value of a re-inrush flag to be described later is referenced. Areset state of the re-inrush flag, that is, a value thereof of zero,indicates that re-inrush control to be described later has not beenexecuted. In this case, the flow of control continues to a step S34 atwhich the re-inrush control is executed for the first time. The in-rushcontrol is executed because, in some cases, the driver feels a sense ofincompatibility if it takes a long time to accomplish a shift change.

On the other hand, a set state of the re-inrush flag, that is, a valuethereof of one, indicates that the shift change was not successful inspite of the fact that the re-inrush control was executed. In this case,the flow of control continues to a step S35 at which the clutch is putin an engaged state without making a shift change. At the same time, there-inrush flag is reset. The flow of control then goes on to a step S36at which the clutch-on control to be described later is executed.

Next, a method adopted for the re-inrush control is explained byreferring to the flowchart shown in FIG. 19. carried out when thesleeves driven by the shift forks into a parallel movement in the axialdirection did not arrive at the normal engagement position, there-inrush control is processing of making a re-movement (re-inrush)attempt to once reduce the movement torque before applying apredetermined torque again to the shift forks.

As shown in the figure, the flowchart begins with a step S40 at whichthe duty ratio of the FETs under the PWM control is reduced to 20%. Tobe more specific, the duty ratio of the FETs (2) and (4) or that of theFETs (1) and (3) is reduced in a shift-up operation or in a shift-downoperation respectively. As a result, the driving torque applied to theshift forks 11 is weakened.

The flow of control then goes on to a step S41 at which a fourth timernot shown in the figure is started to measure time. Then, the flowproceeds to a step S42 to form a judgment as to whether or not the timemeasured by the fourth timer has exceeded 20 ms. If the time measured bythe fourth timer has not exceeded 20 ms, the flow of control continuesto a step S43 at which the Ne control is executed. If the time measuredby the fourth timer has exceeded 20 ms, on the other hand, the flow ofcontrol goes on to a step S44 at which the fourth timer is reset. Theflow of control then goes on to a step S45 at which the re-inrush flagis set. Then, the flow of control returns to the step S13 shown in FIG.16 at which the driving motor 1 is again controlled by PWM at a dutyratio of 100%, applying a large torque to the shift forks as usual.

As described above, in the present embodiment, if a shift change is notmade normally, the torque applied to the shift forks is once weakenedbefore being strengthened again to push forth the sleeves. As a result,the operation to re-inrush the sleeves can be carried out with ease.

Next, essentials and general operations of the Ne control and theclutch-on control cited above are explained by referring to FIGS. 23 and24 respectively prior to a detailed description of the operationsthereof.

As described by referring to FIG. 22, in the present embodiment, whenthe rotation of the shift spindle is started at the point of time T1,the engagement of the clutch is released at a point of time t2 and therotation of the shift spindle is completed at the point of time t3.Later on, at the point of time t4, the control to push the sleeves isexecuted before a transition to the clutch-on control, control to putthe clutch in an engaged state.

In the clutch-on control, the clutch is put in an engaged state slowlyin order to reduce the magnitude of a generated shift shock. In otherwords, it is necessary to lower the rotational speed of the shiftspindle 3. On the other hand, the speed of a shift change is dependenton the rotational speed of the shift spindle 3. It is thus necessary toincrease the rotational speed of the shift spindle 3 in order toimplement a fast shift change.

In order to satisfy the two requirements described above at the sametime, according to the present invention, in a period from the point oftime t4 to the point of time t5, the shift spindle 3 is rotated at ahigh rotational speed until a zone in close proximity to an angularrange to put the clutch in an engaged state is reached whereas, afterthe point of time t5, that is, in the angular range to put the clutch inan engaged state, the shift spindle 3 is rotated at a low rotationalspeed as shown in the time chart of FIG. 22. By executing such two-stagereturn control in the present embodiment, the magnitude of the generatedshift shock and the time it takes to make a shift change can be bothreduced simultaneously.

In addition, in the present embodiment, the timing to put the clutch inan engaged state is controlled to timing optimum for the operation ofthe accelerator pedal carried out by the driver. FIG. 23 is a diagramshowing operational timing charts representing changes of the rotationalangle θ₀ of the shift spindle in the clutch-on control and therotational speed of the engine in the Ne control in a shift-upoperation. On the other hand, FIG. 24 is a diagram showing operationaltiming charts representing changes of the rotational angle θ₀ of theshift spindle in the clutch-on control and the rotational speed of theengine in the Ne control in a shift-down operation.

As shown in FIG. 23, as a general practice in a shift-up operation, thecontrol method comprises the steps of restoring the accelerator pedal,turning on the shift-up switch 51, letting a shift change take place,putting the clutch back in an engaged state and opening the accelerator.In the mean time, the rotational speed Ne of the engine changes as shownby a solid line a. At that time, the shift spindle is controlled asshown by solid lines A and B.

It is also quite within the bounds of possibility, however, that thedriver turns on the shift-up switch 51 without restoring the acceleratorpedal or opens the accelerator before the clutch is put back in anengaged state. In such a case, it is desirable to put the clutch in anengaged state quickly since the driver usually desires a fast shiftchange.

In the present embodiment, changes in engine rotational speed Nerepresented by a solid line b indicate that the driver has turned on theshift-up switch 51 without restoring the accelerator pedal. In thiscase, quick return control of the rotational angle θ₀ of the shiftspindle to put the clutch in an engaged state immediately is executed asshown by a solid line C. On the other hand, changes in engine rotationalspeed Ne represented by a solid line c indicate that the driver hasopened the accelerator with timing preceding timing to put the clutch ina re-engaged state. In this case, quick return control of the rotationalangle θ₀ of the shift spindle to put the clutch in an engaged stateimmediately is executed as shown by a solid line D.

As a general practice in a shift-down operation, on the other hand, asshown in FIG. 24, the control method comprises the steps of restoringthe accelerator pedal, turning on the shift-down switch 52, letting ashift change take place, putting the clutch back in an engaged state andopening the accelerator. In the mean time, the rotational speed Ne ofthe engine changes as shown by a solid line a. At that time, the shiftspindle is subject to two-stage control as shown by solid lines A and B.

In a shift-down operation, however, the engine may be revved. In such acase, it is desirable to put the clutch in an engaged state quicklysince quick engagement of the clutch in such a state will generate ashift shock having a small magnitude.

In the present embodiment, changes in engine rotational speed Nerepresented by a solid line b or c indicate that the engine has beenrevved. In this case, quick return control of the rotational angle θ₀ ofthe shift spindle to put the clutch in an engaged state immediately isexecuted as shown by a solid line C or D respectively.

Next, operations of the Ne control and the clutch-on control forimplementing the two-stage control and the quick return control areexplained in detail. FIG. 20 is a diagram showing a flowchartrepresenting the method of the Ne control carried out at the steps S21,S26, S31 and S43.

As shown in the figure, the flowchart begins with a step S50 at whichthe rotational speed Ne of the engine is measured. The flow of controlthen goes on to a step S51 at which a peak-hold value Nep or abottom-hold value Neb of the rotational speed Ne of the engine measuredso far is updated in dependence on the value of the rotational speed Neof the engine measured at the step S50. Then, the flow of controlproceeds to a step S52 to form a judgment as to whether the shift changeis a shift up or a shift down. If the shift change is a shift up, theflow of control continues to a step S56. If the shift change is a shiftdown, on the other hand, the flow of control continues to a step S53.

At the step S56, the rotational speed Ne of the engine measured at thestep S50 is compared with the bottom-hold value Neb updated at the stepS51 in order to form a judgment as to whether or not the differencebetween the two (Ne-Neb) is equal to or greater than 50 rpm.

This judgment is a judgment as to whether or not the accelerator isclosed in a shift-up operation. A difference (Ne-Neb) equal to orgreater than 50 rpm indicates that the driver has turned on the shift-upswitch 51 without restoring the accelerator pedal or has opened theaccelerator with timing preceding timing to put the clutch in are-engaged state. In this case, the flow of control goes on to a stepS55 to set a quick-return flag F to suggest that the clutch beimmediately put in an engaged state before finishing the processing. Onthe other hand, a difference (Ne-Neb) smaller than 50 rpm indicates thatthe normal control should be continued. In this case, the control of therotational speed of the engine is completed without setting thequick-return flag F.

As described above, if the outcome of the judgment formed at the stepS52 indicates that the shift change is a shift down, on the other hand,the flow of control continues to the step S53. At the step S53, therotational speed Ne of the engine measured at the step S50 is comparedwith the rotational speed Ne1 of the engine stored at the step S12 inorder to form a judgment as to whether or not the difference between thetwo (Ne-Ne1) is equal to or greater than 300 rpm. If the differencebetween the two (Ne-Ne1) is equal to or greater than 300 rpm, the flowof control continues to a step S54 at which the rotational speed Ne ofthe engine measured at the step S50 is compared with the peak-hold valueNep updated at the step S51 in order to form a judgment as to whether ornot the difference between the two (Nep-Ne) is equal to or greater than50 rpm.

This judgment is a judgment as to whether or not the driver has revvedthe engine in the shift-down operation. If the outcomes of the judgmentsformed at both the steps S53 and S54 are an acknowledgment (YES), theflow of control goes on to the step S55 to set a quick-return flag F tosuggest that the clutch be immediately put in an engaged state beforefinishing the processing.

FIG. 21 is a diagram showing a flowchart representing the method of theclutch-on control carried out at the steps S28 and S36.

As shown in the figure, the flowchart begins with a step S70 to form ajudgment as to whether or not the speed of the vehicle is about zero. Inthe present embodiment, speeds of a vehicle up to 3 km/h are regarded asa vehicle speed of about zero. If the speed of the vehicle is aboutzero, the flow of control goes on to a step S72 at which a target angleθ_(T) of the shift spindle 3 is set at a neutral position. The flow ofcontrol then proceeds to a step S73. This flow of control is implementedto make a shift at the time the vehicle is in an all but halted state.In such a case, it is desirable to make a shift change quickly since noshift shock will be generated anyway.

If the outcome of the judgment formed at the step S70 indicates that thespeed of the vehicle is equal to or greater than 3 km/h, on the otherhand, the flow of control goes on to a step S71 at which the targetangle θ_(T) of the shift spindle is set at a second reference angle, anangle differing from an angle, at which the rotation of the shiftspindle 3 is halted by the stopper, by 6 degrees. Since the angle, atwhich the rotation of the shift spindle 3 is halted by the stopper, is+/-18 degrees in the present embodiment, the second reference angle is+/-12 degrees. The flow of control then continues to a step S73 at whichthe current rotational angle θ_(T) of the shift spindle 3 detected bythe angle sensor 28 is input. Then, the flow of control goes on to astep S74 at which the Ne control is executed.

Subsequently, the flow of control proceeds to a step S75 at which a PID(Proportional, Integral and Differential) sum value for PID control isfound. To put it in detail, a proportional (P) term, the integral (I)term and the differential (D) term are found and then added up. The Pterm is the difference (θ₀ -θ_(T)) between the current rotational angleθ₀ detected at the step S73 and the target rotational angle θ_(T). The Iand D terms are the integrated and differentiated values of the P termrespectively. The flow of control then goes on to a step S76 at whichthe PID sum value is used for computing the duty ratio of the PWMcontrol. Then, the flow of control proceeds to a step S77 at which thePWM control is executed.

FIG. 25 is a diagram showing a relation between a PID sum value and aduty ratio. As shown in the figure, a positive PID sum value gives apositive duty ratio while a negative PID sum value provides a negativeduty ratio. The polarity of a duty ratio indicates a combination of FETsto be controlled by PWM. For example, a duty ratio of +50% means thatthe FETs (2) and (4) should be controlled by PWM at a duty ratio of 50%.On the other hand, a duty ratio of -50% means that the FETs (1) and (3)should be controlled by PWM at a duty ratio of 50%.

Subsequently, the flow of control goes on to a step S78 to form ajudgment as to whether or not the time measured by a sixth timer hasexceeded 100 ms. Since the sixth timer has not been started yet tomeasure time initially, the time should have not exceeded 100 ms,causing the flow of control to proceed to a step S79 at which a fifthtimer is started to measure time. The flow of control then proceeds to astep S80 to form a judgment as to whether or not the time measured by afifth timer has exceeded 10 ms. Initially, the time measured by thefifth timer should have not exceeded 10 ms, causing the flow of controlto return to the step S73 to repeat the pieces of processing carried outat the steps S73 to S80.

As time goes by, the time measured by the fifth timer exceeds 10 ms at apoint of time t5 of the time chart shown in FIG. 22. At that time, theflow of control goes on to a step S81 at which the fifth timer is reset.The flow of control then proceeds to a step S82 to form a judgment as towhether the quick-return flag F is in a set or reset state. If thequick-return flag F is in a set state, the flow of control continues toa step S83 to catalog a new target angle set at a value smaller than thepresent target angle by two to four degrees for use in the execution ofquick-return control. If the quick-return flag F is in a reset state, onthe other hand, the flow of control continues to a step S84 to catalog anew target angle set at a value smaller than the present target angle by0.2 degrees.

The flow of control goes on from either the step S83 or S84 to a stepS85 to form a judgment as to whether or not the target angle is close toa neutral angle. If the target angle is not close to the neutral angle,the flow of control returns to the step S73. The pieces of processingcarried out at the steps S73 to S85 are repeated until the target anglebecomes sufficiently close to the neutral angle. Later on, as the targetangle is found sufficiently close to the neutral angle at the step S85,the flow of processing proceeds to a step S86 at which the neutral angleis cataloged as a target angle. The flow of control then continues to astep S87 at which the sixth timer starts to measure time.

If the outcome of the judgment formed at the step S78 indicates that thetime measured by the sixth timer has exceeded 100 ms, on the other hand,the flow of control goes on to a step S90 at which the sixth timer isreset. The flow of control then proceeds to a step S91 at which thequick-return flag F is reset. Then, the flow of control continues to astep S92 at which the PWM control of the switching circuit 105 isterminated.

It should be noted that, if the gear is shifted from a neutral state ata high engine rotational speed in the course of a high-speed cruise, arelatively large engine brake works, imposing an excessively large loadon the engine. In order to solve this problem, in the presentembodiment, there is provided a shift disabling system for preventingthe control shown in FIG. 16 from being executed at a vehicle speedequal to or higher than 10 km/h or an engine rotational speed equal toor higher than 3,000 rpm even if the shift-up switch 51 has been turnedon.

FIG. 11 is a functional block diagram showing the shift disablingsystem. As shown in the figure, the shift disabling system employs aneutral-position detecting unit 81 for outputting an "H"-level signal toindicate that the gear is placed at a neutral position. A vehicle-speedjudging unit 82 generates an "H"-level signal for a speed of the vehicleequal to or higher than 10 km/h. On the other hand, anengine-rotational-speed judging means 83 generates an "H"-level signalfor a rotational speed of the engine equal to or higher than 3,000 rpm.

An OR circuit 84 generates an "H"-level signal the vehicle-speed judgingunit 82 generates an "H" signal or the engine-rotational-speed judgingme generates an "H"-level signal. On the other hand, circuit 85generates an "H"-level signal when the neutral-position detecting unit81 generates an "H"-level signal and the OR circuit 84 generates an"H"-level signal. With the AND circuit 85 outputting the "H"-levelsignal, the shift disabling system prevents the control shown in FIG. 16from being executed even if the shift-up switch 51 has been turned on.

If a shift change is made to a neutral state by mistake at a vehiclespeed equal to or higher than 10 km/h or an engine rotational speedequal to or higher than 3,000 rpm in the course of acceleration from thefirst speed, however, it takes time to accomplish re-acceleration. Thus,a system for disabling a shift to a neutral state in the course of avehicle cruise, for example, at a vehicle speed equal to or higher than3 km/h can be further added besides the shift disabling system describedabove.

According to the present invention, since a shift change is disabled ifthe speed of the vehicle or the rotational speed of the engine and ashift position of the gear satisfy conditions for disabling a shiftchange in spite of the fact that a shift switch has been turned on, theproblem caused by an incorrect operation of the shift switch can beavoided.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are to beincluded within the scope of the following claims.

What is claimed is:
 1. A shift control unit for an electric-power-assist transmission, the electric-power-assist transmission including a shift spindle rotated by a driving motor, an angle sensor for detecting a rotational position of said shift spindle, a transmission mechanism for putting a main clutch in an engaged or disengaged state in a manner which is mechanically coupled with rotation of said shift spindle; and a gear shifting mechanism for switching a gear in a manner which is mechanically coupled with said rotation of said shift spindle, said shift control unit comprising:an engine-rotational-speed sensor for sensing a rotational speed of an engine; a position sensor for sensing a position of said shift spindle; and shift disabling means which is used for disabling a shift change without regard to a shift instruction if the speed of a vehicle is equal to or greater than a predetermined value or the rotational speed of said engine is equal to or greater than another predetermined value and, at the same time, while said position sensor is indicating a neutral position.
 2. The shift control unit for an electric-power-assist-type transmission according to claim 1, wherein in the course of a vehicle cruise, a shift down to a neutral position is disabled.
 3. An electric power-assist transmission comprising:a main clutch; a shift spindle; a driving motor for rotating said shift spindle; an angle sensor for detecting a rotational position of said shift spindle; a transmission mechanism for putting said main clutch in an engaged or disengaged state while coupled with rotation of said shift spindle; a gear shifting mechanism for switching a gear while coupled with said rotation of said shift spindle; and a shift control unit including:a vehicle speed sensor for sensing a speed of a vehicle having said transmission; an engine rotational speed sensor for sensing a rotational speed of an engine driving said transmission; a position sensor for sensing a position of said shift spindle; and shift disabling means for disabling a shift change without regard to a shift instruction if the speed of said vehicle is equal to or greater than a first value or the rotational speed of said engine is equal to or greater than a second value while said gear mechanism is in a neutral position.
 4. The electric power-assist transmission according to claim 3, further comprising means connected with said vehicle speed sensor for generating a hi-level signal when the speed of the vehicle is equal to or higher than 10 km/h.
 5. The electric power-assist transmission according to claim 3, further comprising means connected with said rotational speed sensor for generating a hi-level level signal when the rotational speed of said engine is equal to or greater than 3,000 rpm.
 6. The electric power-assist transmission according to claim 3, further comprising means connected with said position sensor for generating a hi-level signal when the gear mechanism is in a neutral position.
 7. The electric power-assist transmission according to claim 4, further comprising means connected with said rotational speed sensor for generating a hi-level signal when the rotational speed of said engine is equal to or greater than 3,000 rpm.
 8. The electric power-assist transmission according to claim 7, further comprising means connected with said position sensor for generating a hi-level signal when the gear mechanism is in a neutral position.
 9. The electric power-assist transmission according to claim 8, further comprising an OR circuit for generating a hi-level signal when the means connected with said vehicle speed sensor generates a hi-level signal or the means connected with said rotational speed sensor generates a hi-level signal.
 10. The electric power-assist transmission according to claim 9, further comprising an AND circuit for generating a hi-level signal when the means connected with said position sensor generates a hi-level signal and the OR circuit also generates a hi-level signal.
 11. In combination, a shift control unit and an electric-power-assist transmission, said electric-power-assist transmission including a main clutch, a shift spindle, a driving motor for rotating said shift spindle, an angle sensor for detecting a rotational position of said shift spindle, a transmission mechanism for putting said main clutch in an engaged or disengaged state in a manner which is mechanically coupled with rotation of said shift spindle, and a gear shifting mechanism for switching a gear in a manner which is mechanically coupled with said rotation of said shift spindle, said shift control unit comprising:a vehicle speed sensor for sensing a speed of a vehicle having said transmission; means connected with said vehicle speed sensor for generating a hi-level signal when the speed of the vehicle is equal to or higher than a first value; an engine rotational speed sensor for sensing a rotational speed of an engine driving said transmission; means connected with said rotational speed sensor for generating a hi-level signal when the rotational speed of said engine is equal to or greater than a second value; a position sensor for sensing a position of said shift spindle; means connected with said position sensor for generating a hi-level signal when the gear mechanism is in a neutral position; an OR circuit for generating a hi-level signal when the means connected with said vehicle speed sensor generates a hi-level signal or the means connected with said rotational speed sensor generates a hi-level signal; an AND circuit for generating a hi-level signal when the means connected with said position sensor generates a hi-level signal and the OR circuit also generates a hi-level signal; and shift disabling means for disabling a shift change without regard to a shift instruction when said AND circuit generates a hi-level signal.
 12. The shift control unit according to claim 11, wherein said first value is 10 km/h.
 13. The shift control unit according to claim 11, wherein said second value is 3,000 rpm. 